1. Field of the Invention
This invention relates to a radiation image read-out method and apparatus, wherein stimulating rays are irradiated to a stimulable phosphor sheet, on which a radiation image has been stored, and light, which is emitted by the stimulable phosphor sheet when the stimulable phosphor sheet is exposed to the stimulating rays, is photoelectrically detected, an image signal representing the radiation image being thereby obtained. This invention particularly relates to a radiation image read-out method and apparatus, wherein the stimulating rays are linearly irradiated to the stimulable phosphor sheet, and the light emitted by the stimulable phosphor sheet is detected with a line sensor.
2. Description of the Related Art
Radiation image recording and reproducing systems, wherein a stimulable phosphor sheet, which comprises a substrate and a layer of a stimulable phosphor overlaid on the substrate, have heretofore been widely used in practice.
With the radiation image recording and reproducing systems, a stimulable phosphor sheet is exposed to radiation carrying image information of an object, such as a human body, and a radiation image of the object is thereby recorded on the stimulable phosphor sheet. Thereafter, stimulating rays, such as a laser beam, are caused to scan the stimulable phosphor sheet in two-dimensional directions. The stimulating rays cause an exposed area of the stimulable phosphor sheet to emit light in proportion to the amount of energy stored thereon during its exposure to the radiation. The light emitted from the exposed area of the stimulable phosphor sheet, upon stimulation thereof, is photoelectrically detected and converted into an electric image signal by photoelectric read-out means.
The image signal, which has been obtained from the radiation image recording and reproducing systems described above, is then subjected to image processing, such as gradation processing and processing in the frequency domain, such that a visible radiation image, which has good image quality and can serve as an effective tool in, particularly, the efficient and accurate diagnosis of an illness, can be obtained. The image signal having been obtained from the image processing is utilized for reproducing a visible image for diagnosis, or the like, on film or displaying a visible image for diagnosis, or the like, on a cathode ray tube (CRT) display device. In cases where the stimulable phosphor sheet, from which the image signal has been detected, is then exposed to erasing light, and energy remaining on the stimulable phosphor sheet is thereby released, the erased stimulable phosphor sheet is capable of being used again for the recording of a radiation image.
Also, a novel radiation image recording and reproducing system aiming at enhancement of a detection quantum efficiency in the formation of the radiation image, i.e., a radiation absorptivity, a light emission efficiency, an emitted light pickup efficiency, and the like, wherein a novel type of stimulable phosphor sheet is utilized, has been proposed in, for example, Japanese Patent Application No. 11(1999)-372978. With the novel type of the stimulable phosphor sheet utilized in the proposed radiation image recording and reproducing system, the radiation absorbing functions and the energy storing functions of the conventional stimulable phosphor sheet are separated from each other.
The novel type of the stimulable phosphor sheet utilized in the proposed radiation image recording and reproducing system contains a layer of a stimulable phosphor for energy storage, which is capable of absorbing light having wavelengths falling within an ultraviolet to visible region and thereby storing energy of the light having wavelengths falling within the ultraviolet to visible region, and which is capable of being stimulated by light having wavelengths falling within a visible to infrared region and thereby radiating out the stored energy as emitted light.
The novel type of the stimulable phosphor sheet should preferably take on the form combined with a layer of a phosphor for radiation absorption, which is capable of absorbing radiation and being caused to emit light having wavelengths falling within an ultraviolet to visible region. In such cases, energy from the light having wave lengths falling within the ultraviolet to visible region, which light is emitted from the layer of the phosphor for radiation absorption when the layer of the phosphor for radiation absorption is exposed to the radiation carrying image information of an object, (the amount of the energy corresponding to the radiation image information) is stored on the layer of the stimulable phosphor for energy storage. When the stimulable phosphor sheet, on which the radiation image has thus been stored, is scanned with the stimulating rays, the light carrying the radiation image information is emitted from the layer of the stimulable phosphor for energy storage.
The novel type of the stimulable phosphor sheet need not necessarily be provided with the layer of the phosphor for radiation absorption. In such cases, the novel type of the stimulable phosphor sheet is utilized in combination with a fluorescent screen, which is provided with the layer of the phosphor for radiation absorption capable of absorbing radiation and being caused to emit the light having wavelengths falling within the ultraviolet to visible region.
Specifically, in such cases, the fluorescent screen is kept in close contact with the novel type of the stimulable phosphor sheet, and the radiation carrying the image information of the object is irradiated to the fluorescent screen. As a result, the light having wavelengths falling within the ultraviolet to visible region is emitted from the layer of the phosphor for radiation absorption of the fluorescent screen. Also, energy from the light emitted from the phosphor for radiation absorption (the amount of the energy corresponding to the radiation image information) is stored on the layer of the stimulable phosphor for energy storage of the stimulable phosphor sheet. When the stimulable phosphor sheet, on which the radiation image has thus been stored, is scanned with the stimulating rays, the light carrying the radiation image information is emitted from the layer of the stimulable phosphor for energy storage.
Novel radiation image read-out apparatuses for use in the radiation image recording and reproducing systems described above have been proposed in, for example, Japanese Unexamined Patent Publication Nos. 60(1985)-111568, 60(1985)-236354, and 1(1989)-101540. In the proposed radiation image read-out apparatuses, from the point of view of keeping the emitted light detection time short, reducing the size of the apparatus, and keeping the cost low, a line sensor comprising a charge coupled device (CCD) image sensor, or the like, is utilized as the photoelectric read-out means.
Basically, the radiation image read-out apparatuses of such types comprise:
i) stimulating ray irradiating means for linearly irradiating stimulating rays onto an area of a stimulable phosphor sheet, on which a radiation image has been stored, the stimulating rays causing the stimulable phosphor sheet to emit light in proportion to an amount of energy stored thereon during its exposure to radiation,
ii) a line sensor, which comprises a plurality of photoelectric conversion devices arrayed along the linear area of the stimulable phosphor sheet exposed to the linear stimulating rays,
iii) a light collecting optical system, which is located between the line sensor and the stimulable phosphor sheet, the light collecting optical system collecting the light, which has been emitted from the linear area of the stimulable phosphor sheet exposed to the linear stimulating rays, and guiding the collected light toward the line sensor, and
iv) sub-scanning means for moving the stimulable phosphor sheet with respect to the stimulating ray irradiating means, the light collecting optical system, and the line sensor and in a direction (a sub-scanning direction) intersecting with a length direction of the linear area of the stimulable phosphor sheet exposed to the linear stimulating rays (a main scanning direction).
With the conventional radiation image read-out apparatuses described above, it often occurs that the stimulating rays, which have been reflected from a surface of the stimulable phosphor sheet toward the light collecting optical system, are reflected by the light collecting optical system and impinge upon an unread fresh region of the stimulable phosphor sheet, from which unread fresh region the radiation image information has not yet been read out. In such cases, the unread fresh region of the stimulable phosphor sheet is stimulated by the stimulating rays to emit light, and the light emitted from the unread fresh region is detected by the line sensor. As a result, the problems occur in that the image quality of a reproduced radiation image becomes bad due to a fog, or an artifact occurs in the reproduced radiation image.
Also, in cases where the stimulating rays, which have been reflected from the surface of the stimulable phosphor sheet, impinge upon the unread fresh region of the stimulable phosphor sheet and stimulate the unread fresh region, the stimulating rays cannot be utilized correctly for the radiation image readout. Therefore, in such cases, the efficiency, with which the stimulating rays are utilized, cannot be kept high.
The primary object of the present invention is to provide a radiation image read-out method, in which light emitted from a linear area of a stimulable phosphor sheet exposed to linear stimulating rays is collected by a light collecting optical system and guided toward a line sensor, wherein the stimulating rays having been reflected from a surface of the stimulable phosphor sheet are prevented from impinging upon an unread fresh region of the stimulable phosphor sheet, such that image quality of a reproduced radiation image is prevented from becoming bad, and such that an artifact is prevented from occurring in the reproduced radiation image.
Another object of the present invention is to provide a radiation image read-out method, in which light emitted from a linear area of a stimulable phosphor sheet exposed to linear stimulating rays is collected by a light collecting optical system and guided toward a line sensor, wherein the stimulating rays having been reflected from a surface of the stimulable phosphor sheet are prevented from impinging upon an unread fresh region of the stimulable phosphor sheet, such that an efficiency, with which the stimulating rays are utilized, is kept high.
The specific object of the present invention is to provide an apparatus for carrying out the radiation image read-out method.
The present invention provides a radiation image read-out method, comprising the steps of:
i) linearly irradiating stimulating rays onto an area of a surface of a stimulable phosphor sheet, on which a radiation image has been stored, with stimulating ray irradiating means, the stimulating rays causing the stimulable phosphor sheet to emit light in proportion to an amount of energy stored thereon during its exposure to radiation,
ii) collecting the light, which has been emitted from the linear area of the stimulable phosphor sheet exposed to the linear stimulating rays, with a light collecting optical system,
iii) receiving the collected light with a line sensor, which comprises a plurality of photoelectric conversion devices arrayed along the linear area of the stimulable phosphor sheet exposed to the linear stimulating rays, the received light being subjected to photoelectric conversion performed by the line sensor, and
iv) moving the stimulable phosphor sheet with respect to the stimulating ray irradiating means, the light collecting optical system, and the line sensor and in a sub-scanning direction, which intersects with a length direction of the linear area of the stimulable phosphor sheet exposed to the linear stimulating rays,
wherein an end face of an optical device constituting the light collecting optical system, which end face stands facing the stimulable phosphor sheet, is formed into a shape such that the stimulating rays, which have been reflected from the surface of the stimulable phosphor sheet, are reflected by the end face toward the linear area of the stimulable phosphor sheet exposed to the linear stimulating rays or toward a region of the stimulable phosphor sheet, which region is located more forward, with respect to the sub-scanning direction, than the linear area of the stimulable phosphor sheet exposed to the linear stimulating rays.
The present invention also provides a radiation image read-out apparatus, comprising:
i) stimulating ray irradiating means for linearly irradiating stimulating rays onto an area of a surface of a stimulable phosphor sheet, on which a radiation image has been stored, the stimulating rays causing the stimulable phosphor sheet to emit light in proportion to an amount of energy stored thereon during its exposure to radiation,
ii) a line sensor, which comprises a plurality of photoelectric conversion devices arrayed along the linear area of the stimulable phosphor sheet exposed to the linear stimulating rays,
iii) a light collecting optical system, which is located between the line sensor and the stimulable phosphor sheet, the light collecting optical system collecting the light, which has been emitted from the linear area of the stimulable phosphor sheet exposed to the linear stimulating rays, and guiding the collected light toward the line sensor, and
iv) sub-scanning means for moving the stimulable phosphor sheet with respect to the stimulating ray irradiating means, the light collecting optical system, and the line sensor and in a sub-scanning direction, which intersects with a length direction of the linear area of the stimulable phosphor sheet exposed to the linear stimulating rays,
wherein an end face of an optical device constituting the light collecting optical system, which end face stands facing the stimulable phosphor sheet, is formed into a shape such that the stimulating rays, which have been reflected from the surface of the stimulable phosphor sheet, are reflected by the end face toward the linear area of the stimulable phosphor sheet exposed to the linear stimulating rays or toward a region of the stimulable phosphor sheet, which region is located more forward, with respect to the sub-scanning direction, than the linear area of the stimulable phosphor sheet exposed to the linear stimulating rays.
In the radiation image read-out method and apparatus in accordance with the present invention, the optical device, whose end face is formed into the shape defined above, should preferably be a gradient index lens array.
Also, in the radiation image read-out method and apparatus in accordance with the present invention, the end face of the optical device, which end face stands facing the stimulable phosphor sheet, should preferably be formed into a shape such that the stimulating rays, which have been regularly reflected from the surface of the stimulable phosphor sheet, are reflected by the end face toward the linear area of the stimulable phosphor sheet exposed to the linear stimulating rays or toward the region of the stimulable phosphor sheet, which region is located more forward, with respect to the sub-scanning direction, than the linear area of the stimulable phosphor sheet exposed to the linear stimulating rays.
Further, in the radiation image read-out method and apparatus in accordance with the present invention, the stimulable phosphor sheet may be a stimulable phosphor sheet having both the functions for radiation absorption and the functions for energy storage. Alternatively, the stimulable phosphor sheet may be a stimulable phosphor sheet provided with a layer of a stimulable phosphor for energy storage.
In cases where the stimulable phosphor sheet is a stimulable phosphor sheet provided with the layer of the stimulable phosphor for energy storage, the stimulable phosphor sheet may also be provided with a layer of a phosphor for radiation absorption. Alternatively, in such cases, the stimulable phosphor sheet may not be provided with the layer of the phosphor for radiation absorption and may be utilized in combination with a fluorescent screen having the layer of the phosphor for radiation absorption.
As will be understood from the specification, it should be noted that the term xe2x80x9cmoving a stimulable phosphor sheet with respect to stimulating ray irradiating means, a light collecting optical system, and a line sensorxe2x80x9d as used herein means movement of the stimulable phosphor sheet relative to the stimulating ray irradiating means, the light collecting optical system, and the line sensor, and embraces the cases wherein the stimulable phosphor sheet is moved while the stimulating ray irradiating means, the light collecting optical system, and the line sensor are kept stationary, the cases wherein the stimulating ray irradiating means, the light collecting optical system, and the line sensor are moved while the stimulable phosphor sheet is kept stationary, and the cases wherein both the stimulable phosphor sheet and the stimulating ray irradiating means, the light collecting optical system, and the line sensor are moved. In cases where the stimulating ray irradiating means, the light collecting optical system, and the line sensor are moved, they should be moved together with one another.
With the radiation image read-out method and apparatus in accordance with the present invention, the end face of the optical device, e.g. the gradient index lens array, constituting the light collecting optical system, which end face stands facing the stimulable phosphor sheet, is formed into the shape such that the stimulating rays, which have been reflected from the surface of the stimulable phosphor sheet, are reflected by the end face toward the linear area of the stimulable phosphor sheet exposed to the linear stimulating rays or toward the region of the stimulable phosphor sheet, which region is located more forward, with respect to the sub-scanning direction, than the linear area of the stimulable phosphor sheet exposed to the linear stimulating rays, (i.e., the region of the stimulable phosphor sheet, from which the radiation image information has already been read out). Therefore, the stimulating rays, which have been reflected from the surface of the stimulable phosphor sheet, do not impinge upon the unread fresh region of the stimulable phosphor sheet. Accordingly, the image quality of the reproduced radiation image is capable of being prevented from becoming bad. Also, an artifact is capable of being prevented from occurring in the reproduced radiation image.
In particular, with the radiation image read-out method and apparatus in accordance with the present invention, wherein the end face of the optical device, which end face stands facing the stimulable phosphor sheet, is formed into the shape such that the stimulating rays, which have been reflected from the surface of the stimulable phosphor sheet, are reflected by the end face toward the linear area of the stimulable phosphor sheet exposed to the linear stimulating rays, the stimulating rays having been reflected from the surface of the stimulable phosphor sheet are capable of being efficiently utilized for stimulating the stimulable phosphor sheet. Therefore, the efficiency, with which the stimulating rays are utilized, is capable of being kept high.
With conventional techniques, wherein a thin beam of the stimulating rays is deflected, the stimulable phosphor sheet is scanned with one light spot in the main scanning direction, and light detection signal components obtained by photoelectrically detecting the light emitted by the stimulable phosphor sheet are sampled in synchronization with the main scanning, if the stimulating rays, which have been reflected from the end face of the optical device, are returned onto the same main scanning line on the stimulable phosphor sheet in the manner described above, the light emitted from sites on the stimulable phosphor sheet other than sampling points will act as a flare.
However, with the radiation image read-out method and apparatus in accordance with the present invention, the stimulating rays are linearly irradiated onto the stimulable phosphor sheet, and all of the light, which is emitted from the linear area of the stimulable phosphor sheet exposed to the linear stimulating rays, is simultaneously detected with the line sensor.
Specifically, all of the radiation image information having been stored along one main scanning line is read out simultaneously. Therefore, in cases where the stimulating rays, which have been reflected from the end face of the optical device, are returned onto the linear area of the stimulable phosphor sheet exposed to the linear stimulating rays, the thus returned stimulating rays are capable of being utilized efficiently for the radiation image readout, and the adverse effects of the flare do not occur.